There is a great and ever increasing need for shaped materials having good heat insulating properties while possessing sufficient durability and strength at variable temperatures including elevated temperatures. Historically, asbestos fiber has been used in many of such products because of the excellent high temperature properties of asbestos and the relative easy ability to combine the asbestos with other materials, such as wire, elastomers and other polymers. More recently, a demand has arisen for insulating materials that are free or substantially free of asbestos, especially due to the health problems associated with asbestos dust.
Unfortunately, equal replacements for asbestos have not appeared in industry. Glass fibers do not withstand applications involving high temperatures. Ceramic fibers possess good high temperature performance but are difficult to handle and have been used primarily in bulk form.
U.S. Pat. No. 3,395,071 describes the preparation of composite sheets containing asbestos and silicone resins. U.S. Pat. No. 3,835,054 and the reference mentioned therein discuss the use of ceramic fibers to make thermal insulation board.